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arXiv 1603.03437astro-ph.GAastro-ph.CO
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z~1.5的活动星系核：II .利用宽发射谱线估算黑洞质量

Active galactic nuclei at z~1.5: II. Black Hole Mass estimation by means of broad emission lines

Julián E. Mejía-Restrepo, Benny Trakhtenbrot, Paulina Lira, Hagai Netzer, Daniel M. Capellupo

备注：
26 Pages, 15 figures, Accepted for publication in MNRAS
发表信息：
2016MNRAS.460.187M
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摘要：

这是一系列论文中的第二篇，旨在测试超大质量黑洞（SMBH）的质量（$M_{\rm BH}$），吸积率（$\dot{M}$）和自旋（$a_{*}$）如何决定I型活动星系核（AGN）的观测性质。我们的项目利用了VLT/X-shooter观测到的$z\simeq1.55$上的39个未被遮蔽的活动星系核样本，选择这些样本来绘制$M_{\rm BH}$和$L/L_{\rm edd}$中的大范围，并覆盖了最突出的紫外光学（宽）发射线，包括H $α$、H $β$、Mg II和CIV。本文着重于单历元，“维里”$M_{\rm BH}$测定宽发射线，并探讨了不同的连续模拟方法的线宽测量的影响。我们发现，使用一个“本地”的幂律连续，而不是一个物理动机薄磁盘连续导致只有轻微的半高宽的线和相关的$M_{\rm BH}\left({\rm FWHM}\right)$低估。然而，线色散$σ_{\rm line}$和相关的$M_{\rm BH}\left(σ_{\rm line}\right)$受到连续体放置的强烈影响，并且提供比基于FWHM的方法更不可靠的质量估计。我们的分析表明，H $α$，H $β$和Mg II可以安全地用于维里$M_{\rm BH}$估计。另一方面，CIV线在大多数情况下是不可靠的，这可能表明发射该线的气体没有维里化。虽然H $α$和H $β$显示非常相似的线宽，但平均${\rm FWHM\left(MgII\right)}$比${\rm FWHM\left(Hβ\right)}$窄约30%。我们确认最近的几个建议，以提高CIV为基础的质量估计的准确性，依赖于其他紫外线发射线。这种改进并没有减少基于CIV和基于Balmer线的质量估计之间的分散。

英文摘要：

This is the second in a series of papers aiming to test how the mass ($M_{\rm BH}$), accretion rate ($\dot{M}$) and spin ($a_{*}$) of super massive black holes (SMBHs) determine the observed properties of type-I active galactic nuclei (AGN). Our project utilizes a sample of 39 unobscured AGN at $z\simeq1.55$ observed by VLT/X-shooter, selected to map a large range in $M_{\rm BH}$ and $L/L_{\rm edd}$ and covers the most prominent UV-optical (broad) emission lines, including H$α$, H$β$, MgII, and CIV. This paper focuses on single-epoch, "virial" $M_{\rm BH}$ determinations from broad emission lines and examines the implications of different continuum modeling approaches in line width measurements. We find that using a "local" power-law continuum instead of a physically-motivated thin disk continuum leads to only slight underestimation of the FWHM of the lines and the associated $M_{\rm BH}\left({\rm FWHM}\right)$. However, the line dispersion $σ_{\rm line}$ and associated $M_{\rm BH}\left(σ_{\rm line}\right)$ are strongly affected by the continuum placement and provides less reliable mass estimates than FWHM-based methods. Our analysis shows that H$α$, H$β$ and MgII can be safely used for virial $M_{\rm BH}$ estimation. The CIV line, on the other hand, is not reliable in the majority of the cases, this may indicate that the gas emitting this line is not virialized. While H$α$ and H$β$ show very similar line widths, the mean ${\rm FWHM\left(MgII\right)}$ is about 30% narrower than ${\rm FWHM\left(Hβ\right)}$. We confirm several recent suggestions to improve the accuracy in CIV-based mass estimates, relying on other UV emission lines. Such improvements do not reduce the scatter between CIV-based and Balmer-line-based mass estimates.

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